1. Field of Invention
Embodiments exemplarily described herein relate generally to alignment marks used in fabricating semiconductor devices or in assembling display devices. More particularly, embodiments exemplarily described herein relate to an optically recognizable alignment mark.
2. Description of the Related Art
The fabrication of semiconductor devices and the fabrication or assembling of display devices generally involves disposing layers, patterns, display units, and a drive integrated circuit (IC) within a permitted error limit. An alignment mark is used to dispose two or more objects in desired positions. Accordingly, the alignment mark is optically recognized to appropriately select the position of the alignment mark.
FIGS. 1 and 2 are plan views of a conventional alignment mark.
Referring to FIG. 1, the position of an object may be precisely indicated by coordinates along x- and y-axes of a rectangular coordinate system. Thus, the alignment mark 5 has interfaces parallel to an x-axis and a y-axis of a rectangular coordinate system so that x and y coordinates of the alignment mark 5 can be recognized. As illustrated in FIG. 1, the alignment mark 5 includes a cross-shaped main pattern 12 provided in a peripheral region 10. The main pattern 12 has a planar upper surface so that parallel light which is perpendicularly incident to the upper surface can be specularly reflected. The main pattern 12 also has interfaces parallel to the x-axis and the y-axis of the rectangular coordinate system. The position of the interfaces of the main pattern 12 can be recognized using signals of light reflected by the main pattern 12 and the peripheral region 10.
Referring to FIG. 2, because the main pattern 12 has interfaces parallel to an x-axis and a y-axis of a rectangular coordinate system, in which the x-axis is substantially perpendicular to the y-axis, x and y coordinates of the alignment mark 5 can be recognized. The accuracy with which the position of the alignment mark 5 can be recognized depends on the contrast between reflection light (i.e., light that is specularly reflected by the upper surface of the main pattern 12) and scattered light (e.g., light that is reflected by the peripheral region 10). An error in recognizing the interfaces of the main pattern 12 may be increased due to a low contrast between reflection light and scattered light. Accordingly, an alignment error of the object can be increased due to an error in recognizing the interfaces of the main pattern 12.
Although parallel light incident to the main pattern 12 is specularly reflected by the upper surface of the main pattern 12, parallel light incident to the interfaces of the main pattern 12 adjacent to the peripheral region 10 is irregularly reflected. As a result, a contrast between light reflected by the main pattern 12 and light reflected by the peripheral region 10 may be unclear.
Also, a plurality of insulating layers are typically formed on the alignment mark 5. As a result, the brightness of transmission light (i.e., light incident to the main pattern 12 and the peripheral region 10) and reflection light (i.e., light reflected by the main pattern 12 and the peripheral region 10) is degraded because the transmission light and reflection light must pass through the plurality of insulating layers. Thus, the contrast between specularly reflected light and scattered light is lowered. This phenomenon may worsen when a material layer having a non-uniform thickness is formed on the alignment mark 5.
As a result, a measurement time may be excessively delayed to obtain the quantity of light required for discerning the alignment mark 5, and the accuracy of the recognition of the alignment mark 5 can be degraded.